It is often desirable and frequently absolutely necessary to sample or test a portion of tissue from humans and even other animals, particularly in the diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions and other diseases or disorders. Typically in the case of cancer, when the physician establishes by means of procedures such as palpitation, x-ray or ultra sound imaging that suspicious circumstances exist, a very important process is to establish whether the cells are cancerous by doing a biopsy. Biopsy may be done by an open or closed technique. Open biopsy removes the entire mass (excision biopsy) or a part of the mass (incision biopsy). Closed biopsy on the other hand is usually done with a needle-like instrument and may be either an aspiration or a core biopsy. In needle aspiration biopsy, individual cells or clusters of cells are obtained for cytologic examination and may be prepared such as in a Papanicolaou smear. In core biopsy, as the term suggests, a core or fragment of tissue is obtained for histologic examination which may be done via a frozen section or paraffin section.
The type of biopsy depends in large part in circumstances present with respect to the patient and no single procedure is ideal for all cases. However, core biopsy is extremely useful in a number of conditions and is being used more frequently by the medical profession.
A variety of biopsy needles and devices have been described and used for obtaining specimens of tissue. For example, reference is made to U.S. Pat. Nos. 4,651,752; 4,702,260; and 4,243,048 which show biopsy needles of varying types. Additionally, a number of very specialized devices for extracting samples of tissue have been described such as the biopsy device in U.S. Pat. No. 4,461,305, which device is designed specifically for removing a sample of tissue from the female uterine cervix. Other devices have been disclosed which relate to surgical cutting instruments. For example, U.S. Pat. No. 4,589,414 discloses an instrument which is particularly designed to operate in the area of the knee to withdraw tissue chips. Also available are so-called biopsy guns for removing a core of tissue which customarily are spring powered devices and must be cocked with considerable force. When actuated such guns produce a loud snapping noise, combined with a jerking action. Such a biopsy gun may employ a needle set consisting of an inner stylet and an outer tube called a cannula. The stylet is a needle like device with a notched cut-out at its distal end. The cannula in effect is a hollow needle with an angled cutting surface at its distal end which slides over the stylet. When the stylet is forced into tissue, the tissue is pierced and relaxes into the notched cut-out of the stylet. When the cannula is then slid forward, the tissue in the notch of the stylet is sliced off and retained in the notch until the cannula is withdrawn. Examples of such devices are shown in U.S. Pat. Nos. 4,600,014 and 4,699,154. Although such spring powered biopsy guns will remove a core or sample of tissue, they have rather serious disadvantages. For one, they must be manually cocked with a plunger bar. Such "cocking" of the gun requires considerable force and the gun must be cocked for each biopsy cut. A further disadvantage is that the springs provided in the gun accelerate the needles until a mechanical stop position is reached, creating a loud snapping noise and jerking motion which is a problem both to the physician and the patient. This noise and jerking action can cause the patient to jump and in some cases even prevents the physician from striking the intended tissue target. Another disadvantage is that the force and velocity delivered to the stylet and cannula rapidly diminishes when traveling from a retracted to a fully extended position resulting in tissue samples of lower quality.
U.S. Pat. No. 4,940,061 discloses a biopsy instrument which represents a substantial improvement over the aforementioned devices, substantially eliminating the loud snapping noise and jerking motion associated with spring-powered biopsy guns, for example. In the instrument of Pat. No. 4,940,061, an electric motor drives a rotary cam assembly which converts rotary motion to linear motion to sequentially extend and retract a stylet and cannula, and employs electrically actuated stops to control the extension and retraction of the stylet and cannula. Details of the construction and operation of the biopsy instrument are disclosed in U.S. Pat. No. 4,940,061, which is hereby incorporated by reference. Although well suited for many applications, that instrument suffers certain drawbacks, one of them being mechanical wear associated with a limit switch assembly and a toggle assembly which both include stationary wiper plates and spring finger contacts which slide against each other during normal operation.
Accordingly it is a principal object of this invention to provide an instrument for obtaining samples of tissue from tissue masses.
It is another object of this invention to provide an instrument for automatically performing a biopsy of a tissue mass in an accurate and expeditious manner with a maximum of accuracy and a minimum amount of discomfort to the patient.
It is a still further object of this invention to provide an instrument for performing tissue mass biopsies by removing a core or sample of tissue, which instrument eliminates the need for springs and mechanical stops, which is silent in operation and has the ability to effectively penetrate even small tissue masses.
It is another object of this invention to provide an instrument for obtaining tissue samples from tissue masses which instrument requires no manual setting or cocking and which may be "fired" multiple times without any abrupt starts or stops.
It is still another object of this invention to provide a biopsy instrument which includes means to convert rotary motion to sequential, linear motion of substantially constant force and velocity to the means for penetrating and severing a tissue sample from a tissue mass.
These and other objects of the invention will be apparent from the following description and claims.